Electroradiography



Nov. 4, 1958 Filed June 25, 1955 M. L. SUGARMAN, JR

ELECTRORADIOGRAPHY 2 Sheets-Sheet 1 INVENTOR #im l. 60m/mmf, Je.

Nov. 4, 1958 M. L. SUGARMAN, JR

ELECTRORADIOGRAPHY 2 Sheets-Sheet 2 Filed June 23, 1955 No" M mm., n

L Y on ELEC''RGRAPHY Meyer L. Sugarrnan, Jr., Princeton, N. J., assignorto Radio Corporation of America, a corporation of Delaware` Y vApplication .inne 23, 1955, SeriaiNo. 517,476 Claims. (Cl. Z50-65) Thisinvention relates to improved methods and means ior making radiographs(graphic recordings of X-ray images) electrophotographically. Moreparticularly, the invention relates to improved eleetrophotographicmethods and means for electroradiography employing a novel X-raysensitive photoconduetivel material.V Y

Previously radiographs or X-ray prints have normally been made onchemically developed iilm. X-ray processes using such lm are expensiveand time consuming. Furthermore, the methods using iilm require wetprocesses for developing and making prints. Often it is necessary towait several hours before a usableprint is obtained. Normally, in orderto save time in obtaining usable results, the exposed negative isexamined directly.- The black-for-white reversed image involved is muchmore diii'lcult to interpret than a direct positive image,

United States Patent such as that normally provided according to thisinve'ntion.

It is therefore an object of this invention to provide improved methodsand means for electroradiography.

A further object .of the invention is to provide im. proved methods andmeans for producing usable radio-` graphic prints directly upon anexpendable X-.ray sensi.

tive material without the necessity of an intermediate dry or Wettransfer step.

Another object of the invention is to provide improved methods and meansfor directly producing usable radiographic prints quickly andeconomically.

Still another object of the invention is to provide proved methods andmeans for directly producing a usable radiographic print on the objectitself which is being inspected by X-rays. i

Another object of the invention is to provide improved methods and meansfor directly producing usable radiographic prints within a few secondsafter exposure withf out the necessity of an intermediate transfer step.

Yet another object of the invention is to provide proved methods andmeans for directly and continuously producing usable radiographic printsof a series of objects.

These and other objects and advantages of ythe invention are realized bya rapid dry process for directly making immediately usable radiographs.No transfer steps are necessary. In contrast to other dryelectroradiograph systems using photoconductive selenium plates, forexam-v ple, the X-ray sensitive material of the present invention doesnot require a transfer step, and does not require a special master plateWhich must be exposed over and over again, and cleaned betweensuccessive usages. In accordance with the invention, X-ray sensitivephotoconductor-resin mixtures may be coated on paper, plastic, or metalsheets, for example, or directly upon the object to be examined. Anexample of such a material is'tinely divided ZnO dispersed in a siliconeresin binder.. An X-ray image of an object when formed on such a coatingresults in an electrostatic image corresponding to the X-ray image. Theelectrostatic image may be developed with a iinely divided developerpowder and fixed, as by f. to light, are also sensitive Y 2,859,352Patented Nov-v 44. 9.5.3,

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2 #me f SPfaYiilS .with a quick-divins adhesivo sfiato.- r1

The invention will beV described in greater detail yby reference to theaccompanying drawing wherein: i y' Figure 1 is a diagram illustratingthe steps of onevmethod for carrying out the processes of the invention;A Figure 2 is a` sectional, elevational Vview of one embodiment ofapparatus in accordance with the invention for producing an X-ray imageof an object on an X-ray sensitive photoconductive coating according tothe invention; Figure 3a is an elevational viewv of a completely assembled (potted) junction transistor whose internal struc'- ture is notvisible to the unaidedeye; l Figure 3b is a sectional, elevational viewof apparatus for forming an X-ray image on anu X-ray` sensitive photo'-conductive'eoating of the internal lstructure of a transistor such `asshown in Figure 3a; 1

Figure 3c represents a developed electroradiograph ofthe internalstructure ot the transistor shovvn in Figure 3a;

Figure 4 is a sectional, elevational' view of anotherembodiment of theinvention for producing an' X51-.ay image on aphotoconductive coatingaccording'tothe invention;

Figure 5a is an elevational view of another embodi1 ment ,of theinvention wherein an X-ray image of the bone structure of the human armis formed on an Xfray sensitive photoconductive coating directly upon.the outer skin .ofthe arm being X-rayedg Figure 5b shows a developedelectroradiographi print of the bone structure of the human -arm showninFigure 5a; Y A .v

Figure 6 is a partially schematic, elevational Nien! .of anotherembodiment oi the invention .for Daisies radiographs of objects in acontinuous process wherein the objects themselves are carried by anX-ray sensitive photoconductiveqcoated conveyor sheet; V

Figure 7 is a lpartially schematic, elevational vieu oi anotherembodiment of the invention lfor making r 'ographs in a continuousprocess on `an X-ray tive photoconductive-coated conveyor sheet; and

Figure 8 is a partially schematic, `elevational view oi' still anotherembodiment of the invention for rn ing radiographs in a cQntinuQuSPIOPSSS .IQIY 211.1951. objects being inspected. t.

.Similar reference characters are applied vto, similiar elementsthroughout the draw-ing. l

It is known .that fcertain photoooaoiifivs materiels may be employed toproxluce Visible images by iokii! dY tage of the ,electrical response ofouah Het i. *i diations such es visible light. Sugli materials may ,e

charged electrostatically so as to hold a uniform eleetric conductive atthese points. Thus, a latent *ellec/tro charge pattern orresponding tothe incident light e' al charge yin diesem portions of the #here Paitiiois are: portions to the intensity of the liebt fesait/.osi differentportions of the light image. .in yi 'bl l nt eleotrostatio .chargePattern .maville rendered visiti developing with an o losiiisaily.Charged sleoirosoooio row: der which is attracted to and held by thechargepattern. This powder may be permanently iixed to the coatin byheating, Solvent action., supplementary adhesivos, ,or ,othertechniques.

The photooonduoiivo ,Coating-according to .the intenti comprises afinely divided photoconductive material y parsed in anelectrically-insulating film-forming Yoh .o- It has been found that thematerials acjcordingjto ventilos, in addition t9 beingsisaiosteiisallyrs P to X-rays and mayf,

onsive sr. Q

ployed to excellent -advantage'for almost instantaneously providingradiographs. photoconductive material may be coated on paper sheetsorvrolls, metalor plastic films, glass plates or any other mechanicallysuitable surfaces to which 'the' coatingwill. adhere. Because of itscheapneSS, paper is preferred.V s another important feature of theinvention, the X-ray sensiv e photoconductive material maybecoated`directly upon the object to be inspected radiographically. The mixtureused to produce the photoconductive coatmg may include a solvent or themixture may be thermoplastic. I'he mixture may be coated by anyconvenient coating method, for example, Ibyl rolling on with a roller,by screening with a silk or metal screen, by brushing, by v vhirling,`by spraying, or lby stamping. After the mixture is coated, it is dried,for example by evaporation 'of the solvent, or by coolingif themixtureis thermoplastic. Where the :coating is dried by evaporation, heat maybe applied togaccelerate the dryingprocess. Similarly, the

' coating may be chilled where the mixture is thermoplastic and isapplied hot; Y

When the photoconductive .coating is produced-on a resistivity plastics,the backing may be treated so, as to render its surface electricallyconducting. This furnishes a plane immediately below the coating capableof being placed at ground or other desired potential in order tofacilitate charging with a blanket electrostatic charge bef foreexposure. 'Ihis plane may be oating (isolated in potential) during allstages of image production 'other than charging. Preferably a doublecorona discharge is employed to provide ions of opposite charge onopposite sides of the coated insulating base so 'as to obviate thenecessity of rendering Va surface of the insulating base conductive.

` y X-RAY SENSITIVE PHOTOCONDUCTIVE MATERIALS Examples of suitablemixtures for producing an X-ray sensitive photoconductive coating are asfollows:

Example 1.-A mixture of 80 grams of a 60% solution in xylene of siliconeresin GE-SR-SZ, marketed bythe General Electric Company, SiliconeProducts Division, Waterford, New York, 106 grams of toluene and 120grams 'of photoconductive white zinc oxide is ball-milled for aboutthree hours and then applied to the fixed form as described above.lExample 2.-A mixture comprising 100 grams .of powdered photoconductivelead iodide, 100 millilitersof toluene and 60 milliliters, of `a 60%solution of asilicone resin (SR-SZ, source as above) in xylene is`ballmilled until the lead viodide is thoroughly dispersed in-the`plastic-solvent mix and is coated as described above.

` Example 3,-A mixture comprising 100 grams'of finely groundphotoconductive cadmium sulfide and 150 grams of a 35% polystyrenesolution in toluene is `thoroughly mixed for about minutes in a highspeed blender and coated as described above.

Example 4.-A mixturecomprising 60 grams of a 35% solution of polyvinylacetate resin in methanol, '40 grams of CP dry process white zinc oxideand 20 liters of acetone is ball-milled for about one hour and thencoated as described-above. Y

Example 5 .--Equal parts by weight of CP photoconductive white zincoxide and `melted paratiin areintimately mixed and then the moltenmixture applied as described' above and then allowed to cool.

Example 6.--A mixture of three parts by'weight'bf' CP` photoconductivewhite zinc oxide and one part by weight of carnauba wax are melted`together and then coated as described above and then allowed to cool.

Example 7 .-Three parts by weight of CP photocondu tive white zinc oxideand one part by weight of carnauba wax are dissolved in toluene and thencoated as described According to the invention, the

1 polymer resin in acetone.

;. of this solution is mixed with 50 grams .of CP photocon- Example 8.-Two parts by weight of CP photoconducf tive white zinc oxide and onepart by weight of methyl cellulose are `dispersed in f a suitablesolvent and then coated as described above. Y

Example 9.--Seven parts by weight of CP photoconduc--V tive white zincoxide are dispersed in ten parts by weightV of a 10% solution yof avinyl chloride, vinyl lacetate coductive white zinc oxide and thencoated'asV described above.

It w-as found that a mixture of zinc oxide and lead iodide had a greatersensitivity to X-rays than either maf I terial alone according to theexamples above, described.

Vbacking of highly insulating material such as glass or high Thismixture comprised about l0 grams of vPblz` to 90 grams of ZuO inthe-mixture.

FILM-FORMING VEHICLES -I The electrically-insulating, hlm-formingvehicle essential part of the composition and may be chosen from any oneof a number Vof substances. A preferred ilmfV forming vehicle has a highdielectric constant and a high.

dielectric strength. These materials may be naturalor synthetic -resinsor waxes. are the vinyl resins, silicone resins, phenol-formaldehydecompositions, cellulose esters and cellulose others. Shellac is anexample of a naturalmaterial. Examples of suitf able waxes are paran,carnauba wax and beeswax. In;

'il organic binders such as sodium silicate mayalso be used.

Mixtures including one or more vehicles may be used;4

The photoconductor may be suspended in the vehicle in any of severalways. A simpleway is to dissolve the film-forming vehicle in an organicsolventcapable of` effecting the solution and then dispersing thepowdered photoconductorthereon. Alternatively the photoconductor maybedry blended by kneading with the lm'-form ing vehicle heated'to asufficiently high temperature to be rendered plastic. In this case ofwaxes they may be melted.

and the photoconductor mixed with the melt.

The proportion of powdered photoconductor to {ilmforming vehicle in thenal coating may vary over a wide range. The preferred rangesare 50 to90% of photoconductor and 50 to 1,0% of film-forming vehicle. The(2ptimum proportions will be based upon the nature ofthe photoconductor,the lmfforming vehicle andthe results desired. Y

The speed of response of the photoconductive coating is partiallydependent upon the nature of the photocon-,

i" ductor material, the nature of the film-forming vehicle-y and theratio by weight of the film-forming vehicle to that of thephotoconductor. Sincethe speed of response de: pends on a balance ofcharacteristics of these factors, al'

most any desired response may be obtained by a proper selection ofmaterials and compositions. t

A'proper selection of materials and compositions will also designate howlong an electrostatic image may bei stored, since storage of theelectrostatic image `depends at least in part upon the resistivity ofthe coating. Gen'-r erally the higher the resistivity of the coating thelonger the storage time.

DEVELOPER MATERIALS AND APrLrCAriori"` The developer powder may beappliedin any of a` number of ways such as by spraying, dusting,orr-brush-j ing. For application by brushing a convenient brush;

comprises a mixture of magnetic Vcarrier particles,.-forj example,powdered iron and the developer powder.` The mixture is secured in amagnetic iield'to form ardeveloper;

" brush. This method lof development is more completely described by H.G. Greig in U.'S. Patent applicati o n;,V

Serial No. 344,123, tiled March 23,1 1953. V'A carnels hair,A

The mixture is thinned with v Examples of vsuitable resins or otherbrush comprised ,of bristles having suitable tijboelectric propertiesVVto impart the desired charge to theV powder may also be used.

A preferred carrier material for the developer mix in thev magneticdeveloper system consists of alcoholized iron, that is, iron particlesfree from grease and other impurities soluble in alcohol. These ironparticles are preferably relatively small in size, being preferably intheir largest dimension about .002" minimum to .008 maximum.Satisfactory results are also obtained using a carrier consisting ofiron particles of a somewhat wider range of sizes up to about .001 to.020.

Other developing techniques are available and may be employed toadvantage in any of the embodiments of the invention described. Onemethod in particular may actually be preferred because of the sharplyoutlined images produced thereby. This technique is termedk cascadedevelopment and is fully described by Robert C. Mc- Master in an articleentitled New Developments in Xeroradiography published in the Journal ofthe Society for Nondestructive Testing Summer Number, 1951. ln thistechnique the developing powders, consisting of a mixture of linepigment particles and a coarse granular carrier material, are cascadedover the surface of the exposed plate in a rocking developing tray, forexample. The images produced by this technique are high-contrast,sharp-line types rather than those of large areas of nearly constantdensity. Such images, of course, are highly desirable for someapplications in radiography. This is particularly true where it isdesired to accentuate small, but abrupt, changes in image density.

Another method which may be employed to develop the latent electrostaticimages is placing the exposed photoconductor in an environmentconsisting of a cloud of electrically charged particles of powder. Thistechnique is also described in the aforementional article by McMaster.

A preferred developer powder may be prepared as follows: A mixturecomprising 200 grams of 200 mesh Piccolastic resin 4358 (an elasticthermoplastic resin composed of polymers of styrene, substituted styreneand its homologs) marketed by the Pennsylvania Industrial Co., Clairton,Pa., l2 grams of Car-bon Black 6, marketed by the Eimer and Amend Co.,New York, N. Y., l2 grams of spirit Nigrosine S. S. B., marketed by theAllied Chemical and Dye Co., New York, N. Y., and S grams of IosolBlack, marketed by the Allied Chemical and Dye Co., New York, N. Y., arethoroughly mixed in a stainless steel beaker at about 200 C. The mixingand heating should be done in as short a time as possible. The melt ispoured onto a brass tray and allowed to cool and harden, The hardenedmix is then broken up and ballmilled for about 20 hours. The meltedpowder is screened through a 200 mesh screen and is then ready for useas a developer powder. TlLs powder takes on a positive electrostaticcharge when mixed with glass beads or iron powder. It therefore developsan electrostatic image coinposed of negative charges. 2-.4 grams of thedeveloper powder and 100 grams of the magnetic cer-tier material areblended together giving the completed developer Other ratios may beused.

The developer powder may be chosen from a large class of materials. Thedeveloper powder is preferably electrically charged to aid in thedevelopment of the electrostatic latent image. The powder may beelectric ally charged because the powder (l) is electroscopic, or

(2) has interacted with other particles with which it istriboelectrically active, or (3) has been charged from an electricsource such as a corona discharge. Examples of other suitable developerpowders are sulphur, natural and synthetic resins or mixtures thereof.

THE ELECTRORADIOGRAPHIC PROCESS Referring to Figure 1, the Steps .of.the method. .of the invention comprise the formation of an X-.rav imageof an `object to be examined on a blanket-.chargedphgtpconductivecoating. This .coatingmay benna suitable basking Such asPaper cellophane motel. or glass. or upon the object itself. The X-rayimage causes the, photoconductive coating to become more conductive atthe points receiving the radiation so that the charge 'at these pointsleaks off. Thus, the charges remainingifi. e., the dark areas notreceiving X-rays) constitute a latent electrostatic image on the coatingcorresponding to the intensities in the X-ray image. This electrostaticimage is then developed by applying a finely divided tone powderthereto. The powder deposits in densities proportional to Athe, chargepattern, and may be fixed in place by a suitable method, such as byheating.

ELECTRORADOGRAPHIC APPARATUS Referring to Figure 2, an object 2 which isto be, inspected ,is shown as being located between the X-.ray apparatusl and the photoconductive plate A4. The X-rayapparatus is adapted toirradiate the object 2 with X-rays and to project an X-ray image thusformed upon the X-.ray sensitive photoconductive coating 3 which haspreviously been charged with a uniform electrostatic charge. As is wellknown in radiography the precise distance of the object with respect tothe X-ray source is not critical for focusing purposes if the X-raysource is a substantiallyI point source as preferred in this and otherembodiments. of the invention. In general the distance of the objectfrom the point source of X-rays and from the image plane determines onlythe enlargement of the image of the object from impingement of unabsorbed radiation from the X-ray source. Hence, the object 2 may beirradiated with X-rays whether spaced between the X-ra-y source 1 andthe photoconductively coated plate 4 or placed directly on the plate asshown by dotted lines.

The ysensitivity of the photoconduetive coating may be appreciablyimproved by employing a metallic backing plate or intensifying screenjust as in present radiography practice. The intensity of radiation isincreased by such a plate due to the secondary emission of X-raysreflected back to the X-ray sensitive coating.

A latent electrostatic image is formed 0n the photoconductive coating 3which corresponds to the X-ray image. After exposure the plate may thenbe removed and brushed, for example, with a finely divided devoloper aspreviously described to render the electrostatic image visible.

Referring to Figures 3a, 3b, and 3c, a typical use of the invention isillustrated. Figure 3a depicts the normally visual appearance of apotted junction transistor. Such devices are normally encased or pottedin a small metallic cylinder or can or in a solid opaque block of aplastic such as a polymerized epoxy resin. The internal contents undstructure thereof, of course, cannot be visually examined after thedevice is so potted. Usually such completed articles, if inoperative ordefective, must be ldis-assembled to determine the defect. According to.the invention, a transistor such as shown in Figure 3a may beradiographed as shown in Figure 3b. In this embodiment the transistor 6is shown as lying upon the Charged X-ray sensitive photoconductivecoating 3. After irradiation with X-rays and the development and fixingof the electrostatic image of the internal contents of the transistorformed thereby, a radiographic print is obtained as illustrated inFigure 3c. The total time involved in obtainingto the invention, and theeasy and rapid processing in,-

7 volved, it is'fea'sble for the rst time .to make radiographic printsof each completed transistor or other artlcles of manufacture at the endof an assembly line production to detect posisble defects su-ch as thusdescribed.

ELECTRORADIOGRAPHIC PRINTING ON X-RAYED OBJECTS Figure 4 illustrates animportant embodiment of the invention wherein the object 2 to beinspected by X-rays from the X-ray apparatus 1 is coated itself with thephotoconductive material 3. Since the radiograph of the object 2 is tobe formed actually on the object itself, the coating of photoconductivematerial is applied to the side of theV Y 8 paints may be employed.' TheX-ray image on the photoconductive coating results in an electrostatic'image which may be developed and fixed directly upon thev arm itselfv orupon the cast.

radiograph 5 is thus obtained directly upon the memberV As shown inFigure 5b a X-rayed showing not only the extent .of the fracture 'butalso its direction and location. Such a print is available withinseconds after Vexposure to` the X-rays. desired to keep the areaavailable for further radiographs,

the fixing step may be omitted and after the fracture has been set thephotoconductive coating with its visible image may be removed as byblowing off, by erasing with a magnetic brush after light exposure, orby washing with water or alcohol. Tor make later radiographs either onthe the coating re-used immediately or at a future time by ice-charging,re-exposing with X-rays or visible light, and re-developing. Additionalimages may also be added by incidence of additional images of suitablespectral characteristics on non-image portions of the coated area.

By using the method of coating the object as illustrated in Figure 4,many advantages heretofore unobtainable with any previously known X-rayprocess may be realized. A radiograph of the contents of any opaquecontainer may thus be printed upon the surface of the container showingnot only the structure therein but also the shape, size, and position.This embodiment of the invention may be practiced to advantage in otherapplications such as in detecting flaws in metals which have been castor machined. Here a radiograph showing the aws may be printed directlyupon the metal itself where the flaw occurs. As pointed out inconnection'with Figures 3a, 3b, and 3c the internal structure of devicessuch as a transistor showing size, position and defects, if any, can beprinted directly upon the opaque casing in an assembly line technique.

Another important use of the embodiment wherein the X-ray sensitivephotoconductive coating is applied directly to the object to beradiographed is in the eld of medicine. Referring particularly to Figure5a, a human arm is depicted which may have a bone fracture, for example.Heretofore prior to the setting of the bones it was necessary to X-raythe arm using chemically-developed lilm. After development of the film,which may consume several hours, the bone could properly be set byreferring to the film. Furthermore, it is often desirable to have anindication on the limb itself representing the direction and location ofthe fracture. By prior methods this was accomplished by referring to theX-ray film in order to manually draw with an indelible pencil theapproximate location and direction of the fracture. Finally, after thefractured arm or leg has been set, a cast is often placed thereon.

As` shown in Figure 5a, the photoconductive coating may be applieddirectly onto the arm or to the outside of the cast on the side oppositethe side to be exposed to X-rays. In order to charge the photoconductivecoating 3 it is necessary to provide a conducting path to groundimmediately `below the photoconductive coating. The skin itself may besuiciently conductive to provide this ground. Other additional groundingmeans may be easily and cheaply provided by first coating the skinsurface with a thin lm 7 of a colloidal graphite dispension such as oneof the Dag dispensions marketed by the Acheson Colloid'Company, PortHuron, Michigan. Likewise'silver platelet suspensions or othervconducting tures thereof. An alternative indicia marking means;

arm or a cast it is only necessary to re-charge vthe photo-.2 .Y

conductive material and re-expose andV develop.

ELECTRORADIOGRAPrnC CONTINUOUS PROCESSES Referring now to Figure 6, acontinuous process of l electroradiography is shown for printingradiographs of a' continuous series of objects 10 directlyV uponanAX-'ray' Y sensitive photoconductive tape 12 which carries theobjects.

The paper which is coated with X-ray sensitive photo-.wV

This

conductive material is supplied by the roll 14. paper may comprise anygrade of paper of reasonable strength. The coating comprises a nelydivided photo-y conductive material dispersed in anelectrically-insulating film-forming vehicle such as previouslydescribed.

The iirst operation is that of depositing a blanket electro- 'i staticcharge upon the photoconductive coating by means of the corona dischargeapparatus 20 and a grounded metal plate 22. The paper passes between thecorona discharge. apparatus 20 and the grounded metal plate 22 which isnecessary to aid in establishing the electricl lield necessary toproduce a corona discharge. A grounded conductive roller may be usedinstead of the plate 22. The corona discharge apparatus may comprisethree .003" diameter wires placed about 0.5" apart and-A about 0.5 fromthe'surface to be charged.

The objects 10 to be electroradiographed are then placed on the chargedphotoconductive surface of the paper 12 and as the objects and the paperpass beneath the X-ray source 1 they are irradiated thereby. The

X-ray image of the objects thus formed on the X-ray sensitivephotoconductive coating in turn forms a latentk electrostatic imagecorresponding thereto.

After exposure to the X-rays the objects may then be removed whilethepaper continues to travel to the,

developing station. The latent electrostatic images formed on thecoating are brushed with a'rotary mag-1 netic brush 24. The magneticbrush may comprise a rotatable, circular magnet having attached theretoa mixture of finely divided magnetic carrier particles and linelydivided developer particles. As the brush contacts the electrostaticimages, the developer powder particles adhere thereto in a patterncorresponding to the electrostatic image. scribed developer mix whichincludes a thermoplastic developer powder. Y

After development the paper with its developed images thereon passes aheat source 26 which `applies heat to the developed images, fusing theimages and causing Y them to adhere to the photoconductive coating,thereby fixing the developed images to the paper 12. The heat source 26may comprise a resistance heater or an infrared lamp. Thereafter thepaper is wound upon a take-up reel 28.

A permanent radiographic record thus is obtained ofl each object comingoif an assembly line production-type process, for example. In order toidentify each object with its respective radiograph, X-ray opaqueindicia may be placed on the objects so as to not obscure the strucfhusfer-md" If it isY It is preferred to use the previously deassegna'terial is also light-sensitive.' Thus the index information may be addedby exposing the photoconductive coating atsome convenient point to avisible light imageV using a `suitable optical arrangement.

VAnother embodiment of theinvention is shown in Figure 7 wherein aVcontinuous series of objects 10 may be electroradiogra-phed upon anX-ray sensitive photoconductive tape 12. In this embodiment the objectsare not carried upon the X-ray sensitive tape itself but are transportedby means of an X-ray transparent belt 30. Thus as the objects 10 arecarried past the X-ray source 1, the X-ray images formed thereby arefocused upon the X-ray sensitive paper which is being transporteddirectly beneath the X-ray transparent-belt 30. As before the X-raysensitive paper 12 may be supplied already coated from the reel 14;Alternatively the paper may be fed uncoated past acoating-application-trough 16 and coated thereby and then dried as itpasses the heating source 18. Either an infrared lampV or an electricalresistance element may comprise the heating source 18. Other rapiddrying means may beemployed. Charging may be accomplished by means ofa'grounded metal roller 22 instead of but for the same purpose as thegrounded plate described in connection with Figure 6. After theformation of the latent electrostatic image corresponding to the X-rayimages, the paper is transported past the developer 24 and the fixer 26.This embodiment is especially advantageous where the weight of theobjects to be electroradiographed is too great to be supported by theX-ray sensitive paperitself. In order to form sharp X-ray images of theobjects upon the X-ray sensitive paper, the travel speed of both theconveyor belt 30 and the paper 12 must be substantially the same.Otherwise due to the movement of the objects 10 at a dierent rate withrespect to the movement of the paper 12 during image formation blurringwould occur. The synchronization of the belt conveyor 30 and the X-raySensitive paper 12 may be accomplished by driving both the conveyor andthe paper from the same motor 32 by like-diameter pulleys on the samemotor shaft, and like-diameter pulleys on the paper take-up reel 28 andthe conveyor belt driver 34. The X-ray transparent belt 30 may be madefrom any suitable X-ray transparent material having sufficient strengthto support objects of given weights. An example of such a material isplasticised plastic-laminated fiberglass or cloth, or a thin Valuminumor stainless steel belt. A suflicient intensity of X-rays to penetratethe belt completely should be employed.

In this embodiment a permanent radiographic print of each object isobtained. As explained before, the identication of a particular objectwith its image may be accomplished by placing X-ray opaque indicia uponthe objects in some convenient location so as to not obscure any of thestructure of the objects or by exposing to a Visible light image of theindexing information.

Referring to Figure 8, a continuous process is shown for printingradiographs directly upon the objects to be examined by X-rays. Theobjects 10 are carried upon a continuous X'ray transparent conveyor 30which may be made of any suitable X-ray transparent materialsufficiently strong enough to support the objects. The conveyor 30 firstcarries the objects past a spray nozzle 16 which sprays thephotoconductive coating completely over the upper surface of theobjects. This coating comprises a nely divided photoconductive materialdispersed in electrically-insulating hlm-forming vehicle such aspreviously described.

The photoconductive coated objects are then fed past an infrared lamp 18or other heating means where the coating is dried. The next operation isthat of depositing a blanket electrostatic charge upon thephotoconductive coating on each object by means of the corona dischargeapparatus and 22 such as described previously. If the objects themselvesare electrically conduct- 1,0 ing, a single corona discharge issuificient. lilowevei',` the objects are relatively-thinandvflat but notelectrically conductive, a -second corona apparatus 22 furnishing Aablanket charge of lopposite electrical sign on thereverse side of theobject may be aligned opposite the corona unit 20. The objects thus passbetween thel corona discharge apparatus 20 and the corona dischargeapparatus 22 which is necessary to aid in'establishing the electricaleld necessary to produce a uniform surface charge.

The objects are thereafter passed over the X-ray source 1 and irradiatedwith X-rays therefrom. The X-ray image of the objects are thus formed onthe X-ray sensi,-` tive coating on the objects themselvesand these Xray`images in turn form latent electrostatic .images corresponding theretoon the photoconductive coating on the objects.

rI he latent electrostatic images formed on the coatings on each objectare then brushed with a rotarymagneft'ic brush 24, or developed by othersuitable v means"such as have been described. The magnetic brush (whichmay comprise a rotatable cylindrical magnet having attached thereto amixture of finely divided magnetic carrier Vparticles and finely divideddeveloper particles) contactsthe electrostatic images on the objects.The developer powder particles adhere to the images in a patterncorresponding thereto. Preferably a developer may be employed whichincludes a thermoplastic developer powder.

The last operation is performed as the conveyor 30 carries the objectswith their developed images thereon past an infrared lamp 26 which fusesthe images and causes them to adhere to the photoconductive coating oneach object. The developed images are thereby permanently xed to theobjects themselves.

It has been found that the exposure time for the X-ray sensitivephotoconductive materials such as zinc oxide or lead iodide is of thesame order of magnitude as the exposure time of industrial X-ray lm(type M, such as supplied by Eastman Kodak Co., Rochester, New York, forexample).

It should be understood that the various charging techniques describedare interchangeable and are primarily dependent upon the electricalcharacteristics of the material which is coated photoconductively. Ingeneral if the objects to be radiographed according to the invention arethin but not electrically conductive the double corona dischargeapparatus described in connection with Figure 8 is to be preferred.

There thus has been described economically inexpensive methods and meansfor making radiographic prints either on a separate recording medium orupon an object being inspected radiographically. Many modifications ofthe invention may be made, as has been demonstrated, without departingfrom the scope of the invention. Because of the demonstrated versatilityof the novel X-ray sensitive material according to the invention,

many uses heretofore impossible or impractical may be realized. Theinstant specication has representatively illustrated the range ofpossible applications of the instant invention.

v What is claimed is:

l. A method of electroradiography comprising the steps of: exposing anelectrostatically charged object to be electroradiographed having anX-ray sensitive coating thereon to an X-ray image of said object, saidcoating consisting at least of a finely-divided photoconductive materialdispersed in an electrically-insulating film-forming vehicle, anddeveloping said electrostatic image.

2. A method of electroradiography comprising the steps of: coating atleast one side of an object to be electroradographed with afinely-divided photoconductive material dispersed in anelectrically-insulating filmforming vehicle, providing said coating witha blanket electrostatic charge, irradiating the side of said objectwhich is uncoated and opposite said coated side with X- rays whereby theX-ray image of said object which is electroradiogra'phed, means adjacentsaid conveyor for coating at least one side of each of said objects onsaid conveyor with a finely-divided photocondctive materiall dispersedin an electrically-insulating` hlm-'forming vehicle, means adjacent saidconveyor for electrostatically charging 'said coating on said objects,X-ray means adjacent said conveyor for kforming an X-ray image of each'of said objects on said coating of each object as'said objects arecarried thereby, each ofv said X-ray images forming on said coating ofeach of said objects a latent electrostatic image correspondingrto saidX-ray image thereon, and means adjacent said conveyor for developingsaid electrostatic images as said conveyor passes thereby.

,g 4,.',Electroradiograph apparatus comprising'an X-ray transparentconveyor adapted to transport objects to be electroradiographed, meansVadjacent said conveyor for coating at least Vone side of'each of saidobjects on said conveyor with a Iinely-divid'ed photoconductivematerial, means adjacent said conveyor for electrostaticallychargelectro#V static image corresponding to said X-ray image, and de`ing said'c'oating'on' said objects, X-ray means adjacentV said conveyorfor yforming an X-ray imagev of eaclzfof' saidV objects onsaid'co'atingof eachY object as said obj; jects are ycarried thereby,`each 4ofsaid X-ray inag'es' formingon saidcoating of each of saidobjects a latentVV electrostatic'irnage corresponding to said X'rayimage thereon', means adjacent said conveyor `for developing saidelectrostatic images with a finely-divided developer as said conveyorpasses thereby, and means for iiXingvsaidy developed images. Y

5. The'method of claim 2 wherein said photoconductive' material iszincoxide.`

References Cited inthe iile of this patent UNITED'srATES PATENTS2,221,776 Carlson Nov.

2,666,144 Schatert et al. ..,Jan. V12,` 1954;. 2,701,764 ,Carlsonr Feb.8, 1955; 2,728,021

ciety of America, August 1955, vol. 45,V No.V 8, pages Y.

6474650 especially p. 647. Y

2. A METHOD OF ELECTRORADIOGRAPHY COMPRISING THE STEPS OF: COATING ATLEAST ONE SIDE OF AN OBJECT TO BE ELECTRORADIOGRAPHED WITH AFINELY-DIVIDED PHOTOCONDUCTIVE MATERIAL DISPERSED IN ANELECTRICALLY-INSULATING FILM FORMING VEHICLE, PROVINDING SAID COATINGWITH A BLANKET ELECTROSTATIC CHARGE, IRRADIATING THE SIDE OF SAID OBJECTWHICH IS UNCOATED AND OPPOSITE SAID COATED SIDE WITH XRAYS WHEREBY THEX-RAY IMAGE OF SAID OBJECT WHICH IS THEREBY FORMED ON SAID COATINGPRODUCES A LATENT ELECTROSTATIC IMAGE CORRESPONDING TO SAID X-RAY IMAGE,AND DEVELOPING SAID ELECTROSTATIC IMAGE.